Background

Acute basilar artery thrombosis is associated with a poor prognosis.
[1] However, the advent of high-quality, reliable, and noninvasive technology (eg, magnetic resonance imaging [MRI]) has made its diagnosis possible even in subjects with mild symptoms (see the image below). This has illustrated that some patients have an acute partial occlusion or a slow progressive occlusion with limited ischemic injury and, therefore, a better prognosis. (See Etiology and Workup.)

Although outcomes continue to be poor in patients with basilar artery thrombosis, advances in pharmacologic and mechanical thrombolysis and in endovascular therapy may reduce the mortality and disability rates associated with this disease. (See Prognosis, Treatment, and Medication.)

Vertigo is one of several common presenting symptoms associated with basilar artery occlusion. See Vertigo: 5 Case-Based Diagnostic Puzzles, a Critical Images slideshow, to help recognize diagnostic clues in vertigo cases.

Complications

Complications of basilar artery thrombosis can include the following (see Prognosis, Presentation, and Workup):

Aspiration pneumonia

Myocardial infarction

Deep vein thrombosis and pulmonary embolism

Patient education

Anatomy

The basilar artery is the most important artery in the posterior circulation. It is formed at the pontomedullary junction by the confluence of both vertebral arteries. It lies on the ventral surface of the pons and, throughout its course, gives off the median, paramedian, short, and long circumferential branches.

Anterior inferior cerebellar artery

The branch of the basilar artery with the larger circumference is the anterior inferior cerebellar artery. It normally arises at the junction of the proximal and middle third of the basilar artery and supplies the lateral pontine tegmentum, brachium pontis or middle cerebellar peduncle, flocculus, and a small part of the anterior cerebellum. The internal auditory artery usually arises from the anterior inferior cerebellar artery; however, it may also arise as a direct branch of the basilar artery.

Posterior cerebral artery

The terminal branch of the basilar artery is the posterior cerebral artery (PCA); it supplies the midbrain, the thalamus, and the medial aspect of the temporal and occipital lobes. Proximal to its bifurcation into the terminal branches (ie, PCA), the basilar artery gives off the superior cerebellar arteries that supply the lateral aspect of the pons and midbrain and the superior surface of the cerebellum.

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Pathophysiology

Given the anatomy of the posterior circulation and the circle of Willis, the clinical manifestations of basilar artery thrombosis depend on the location of the occlusion, the extent of the thrombus, and the collateral flow. Normally, the blood flows in an anterograde fashion from the vertebral arteries to the basilar artery up to its terminal branches. This pattern of flow may vary.

If the proximal segment of the basilar artery is occluded and the occlusion has resulted from a slowly progressive stenosis, collateralization occurs within the cerebellum into the circumferential branches of the basilar artery. Additionally, flow can be reversed from the PCAs into the distal basilar artery.

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Etiology

The risk factors for basilar artery thrombosis are the same as those seen generally in stroke. The most common risk factor is hypertension, which is found in as many as 70% of cases. It is followed by diabetes mellitus, coronary artery disease, peripheral vascular disease, cigarette smoking, and hyperlipidemia.

The mechanism of stroke in basilar artery occlusion differs depending on the segment of the vessel involved. Atherosclerotic occlusive disease predominantly affects the midsegment of the basilar artery, followed by the vertebrobasilar junction.

Embolism, either from a cardiac or arterial source, is much more frequent in the distal third of the basilar artery and the vertebrobasilar junction.

Arterial dissection is much more common in the extracranial vertebral artery. It has been associated with a previous neck injury or chiropractic manipulation. Intracranial dissections are very uncommon.

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Epidemiology

Occurrence in the United States

The frequency, incidence, and prevalence of basilar artery occlusion are not known. Although basilar artery occlusion has been reported in 2 per 1000 autopsy cases, basilar artery thrombosis may, in stroke registries, explain as many as 27% of ischemic strokes occurring in the posterior circulation.

Race-, sex-, and age-related demographics

Atherosclerotic basilar artery stenosis, like stenosis of any other intracranial artery, is more frequent in the African American and Asian populations than in white populations. The male-to-female ratio for basilar artery thrombosis is 2:1.

Basilar artery occlusion secondary to atherosclerosis is most prevalent in the sixth and seventh decades of life. Occlusion of the distal basilar artery is usually secondary to embolism and is most frequent in the fourth decade. Women with basilar artery occlusion are typically older than men.

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Prognosis

Patients with acute basilar artery occlusion have a mortality rate of greater than 85%, although the mortality rate may be as low as 40% in patients with recanalization. Good functional outcomes can be expected in as many as 24-35% of patients treated with intravenous (IV) or intra-arterial thrombolysis, respectively. For symptomatic patients who survive, the risk of recurrent stroke is 10-15%.

Morbidity and mortality

The prognosis for basilar artery occlusion is generally poor, with the mortality rate for this condition consistently reported at greater than 70%. However, the prognosis depends on several factors, including the following
[2] :

Decreased level of consciousness

Dysarthria

Pupillary abnormalities

Bulbar symptoms

Diplopia

Bilateral cerebellar lesions

Tetraplegia

Cardiac cause of embolism

Up to 90% of patients with no such factors have a good functional outcome, while in one study, all patients with such factors either died or had severe disability.
[2]

Recanalization is an important requisite for a good functional outcome.
[3] A Barthel index of 85 can reportedly be achieved in as many as 58% of patients with vessel recanalization. Recanalization may decrease the mortality rate from basilar artery thrombosis by 50%, although the outcome in a series of patients with the condition who were treated with antithrombotics was similar to that reported in the available series of patients treated with thrombolytic therapy.

A study by Schonewille et al involving 82 patients with symptomatic basilar artery occlusion found that conventional therapy with antiplatelets, anticoagulation, or both was associated with a poor outcome in almost 80% of patients. The case fatality are in the study was 40%, with 65% of survivors remaining dependent (Rankin score 4-5).
[4]